The present invention relates to the field of devices for measuring the angular position of a rotating axis, known as angular pick-offs. These devices which supply the measured magnitude or quantity in the form of a direct current or voltage proportional to an angle are more particularly used in servomechanisms as position indicators.
The direct current angular pick-off are circular resistors having a moving slider, often called potentiometers and constituted by an either solid or coiled wire resistance track along which can move with gentle friction a conductive slider. The main defects of this type of pick-off are the wear to the track and the slider, the poor and erratic contacts determining arcs or parasitic disturbances and the mechanically hysteresis on changing the rotation direction.
For this reason, in applications where a high level of reliability and a long incident-free operation are sought, it has been proposed to use devices without components subject to mutual friction or contact and which operate by purely inductive coupling, which can vary as a function of the change in the angular position to be measured.
Certain of these known inductive devices are called resolvers. These are rotating machines having a stator and a rotor, both being constituted by a magnetic circuit and a pair of electrical windings defining two north - south magnetic axes at right angles. These machines can be used for numerous applications, for example the remote transmission of the angular position of the rotor thereof, the reception being ensured by an identical receiving machine, whereof the rotor restores the same position.
When the angular pick-off is operating a single winding of the stator and rotor is necessary, and for a given rotation angle of value .theta. the voltage induced in the rotor winding by an alternating voltage applied to the stator is linked with variations in the angle .theta..
The said induced voltage normally has to undergo a rectification in order to obtain the sought direct current voltage.
However, proportionality between the voltage and angle .theta. is only obtained for the small angular variations, the voltage supplied by a resolver-type pick-off being proportional to the trigonometric sine line of angle .theta..
In order to increase the proportionality range between the voltage and the rotation angle, it has been proposed to use the second winding normally present in the rotor of a synchro-resolver by collecting the alternating voltage induced at its terminals and, after amplification, applying it by a negative feedback loop in parallel to the primary supply winding. In order to obtain a suitable choice of the amplification gain, it is possible to increase the proportionality range or the linearization.
However, this solution involves the use of two rotor windings at an angle of 90.degree., requiring the costly and difficult construction of two identical windings defining two magnetic axes at precisely 90.degree.. Moreover, the connecting in parallel of the output of one amplifier to a winding which is already connected to an alternating supply source leads to a complicated construction in order to prevent insulation problems.